1. Field of the Invention
The present invention relates to a control device for a hybrid vehicle that includes an engine, which is adapted to allow a partial cylinder deactivation operation, and in particular, the present invention provides a control device for a hybrid vehicle which enables warming of a battery device when the vehicle is either in a partial cylinder deactivation state or in an all-cylinder operation state.
2. Description of the Related Art
As disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 2001-57709, an engine control device is known which performs warming of a battery when the vehicle runs in a cruise mode and when at least one of the temperature of the battery and the temperature of engine cooling water does not reach a predetermined temperature, in such a manner that the engine control device increases the amount of power generation during the cruise mode and continues charging into the battery until a time at which both the temperature of the battery and the temperature of engine cooling water reach the predetermined temperature. In this vehicle, when it is determined that the battery cannot accept any more charging energy, a vibration control is executed by operating a motor so as to generate electrical power or so as to assist power of the engine so that periodic variation in driving power of the engine is restrained, and thereby vibration of the vehicle due to variation in driving power of the engine is restrained.
However, in such a conventional control process described above, a problem is encountered in that a load applied to the engine is increased, and thereby fuel economy is degraded because warming the battery is performed by charging the battery by power generation.
In recent years, a type of hybrid vehicle is also known which employs a cylinder deactivation technique in order to further improve fuel economy. In this technique, when the hybrid vehicle runs in a decelerating state and fuel supply is suspended so as to place cylinders of the engine in a non-burn state, intake valves and exhaust valves of some of the cylinders are maintained to be closed so that friction losses in the deactivated cylinders are reduced, the amount of power generation is increased by an amount corresponding to reduced friction loss so that the amount of energy charged into the battery is increased, and the increased electrical energy is used for operating the motor so that a load on the engine is reduced, and thereby fuel economy is improved.
However, when the above-mentioned warming control for a battery is applied to the hybrid vehicle which allows execution of a cylinder deactivation operation, because a load applied to the engine is increased during power generation in the cylinder deactivation state, an all-cylinder operation must be resumed by canceling the cylinder deactivation operation; therefore, a problem is encountered in that frequency of executions of cylinder deactivation operation is reduced, and fuel economy is not improved. In addition, because an energy management is employed, in which frequency of power generation operations is increased under a low temperature condition than under a normal temperature condition, when, for example, the battery is maintained in a substantially fully charged state, and when a state of charge of the battery reaches an upper limit while the vehicle runs on a down slope, a regeneration operation is restrained, and thereby energy corresponding to restriction of regeneration cannot be recovered, and the energy is lost.